This invention relates to a flat bottom plastic bag and to a method for constructing such a bag, and more particularly to a method for constructing a flat bottom in a plastic bag which has a laterally sealed bottom end and a pair of opposing pleated sides.
Flat bottom substantially free standing bags are widely utilized both in the grocery and fast food industries. Presently, however, most such bags are constructed from paper. As a result, they tend to tear rather easily. Moreover, spilled liquids and grease can leak through the paper and damage clothing, automobile upholstery or other items against which the bag rests. The paper bags are also heavier and occupy more storage space than comparable plastic bags. Thus, the cost of shipping and warehousing of paper bags is more expensive than for plastic.
Plastic bags provide improved strength and are largely leak resistant. But, in order for plastic bags to be considered as an alternative to paper bags, in most market areas they must have a flat bottom and must be folded to closely resemble the common paper bag. However, to date considerable difficulties, both economic and physical, have been encountered in constructing a flat bottom for such a bag.
One known plastic bag employs four diagonal heat seal on the gusset areas. These seals are commonly referred to as chevron seals and are used in addition to the transverse bottom seal. These chevron sealed gusset areas from a portion of the flat bottom when the bag is opened. Unfortunately, very often a flat bottom is only achieved after extra manipulation by the operator. A further drawback to this type of bottom pertains to the length of the bag. Specifically, the bottom extends the length of the bag. The plastic bottom is longer than its paper counterpart. Therefore, conventional plastic bags will not physically fit the existing shelf space. The causes an inconvenience at the stores.
Another existing square bottom plastic bag is constructed by cutting flaps, then folding and gluing these flaps to form a flat bottom. A patch is then glued over the bottom to hold it together. Such bags are usually more expensive than comparable paper bags. Moreover, the flaps create areas on the bottom which are not sealed and allow the bottom to leak. As a result, the major advantage which plastic bags normally enjoy is lost.
Previous methods of constructing flat bottom plastic bags have provided generally unsatisfactory results. Heretofore inadequate and unreliable means have been used for gripping the opposing surfaces of the bag and separating the pleats. As a result of manipulating the bag surfaces, a vacuum is generated within the bag which deforms the intended fold lines. Thus, a generally inferior bottom is formed. Moreover, prior techniques do not permit trapped air to escape from the bottom as it is flattened. Consequently, the bag is liable to burst as pressure is applied during the flattening operation.
During the formation of a single sealed flat bottom plastic bag, one which truly resembles the paper bag, pockets are formed in the pleated sides. These pockets become part of the bottom. Unfortunately, when manufactured in this way, the pockets tend to reopen or separate when objects are placed inside the bag. Therefore, the desired square bottom configuration is lost.